THIS INVENTION relates to a wrench for use with drilling apparatus.
The invention relates in particular to a wrench for use with drilling apparatus of the type used for drilling holes in the ground and where the drill bit comprises a drilling segment that defines the leading end of the drill bit and a plurality of extension segments that can be linked with the drilling segment for extending the length thereof. Such a drill bit generally includes also a segment, referred to as a distance piece, that links the remainder of the drill bit to the chuck of the drilling apparatus. Holes to be drilled in the ground with a drill bit as described are required in relation to various mining and other applications.
A drilling operation thus provides for a hole to be drilled to a depth permitted by the length of a drill bit at a particular time, whereafter an extension segment is inserted in line with the drill bit which, in effect, permits the drilling apparatus to be retracted by a distance equal to the length of the extension segment and then for drilling to continue until a further extension segment must be inserted in line with the drill bit.
Insofar as this mode of drilling a hole in the ground is well known, this is not described in further detail herein.
The drilling segment, the extension segments and the distance piece of a drill bit as herein envisaged, hereinafter merely referred to as the drill bit segments of a drill bit, are axially connected with one another via complementary threads in a spigot and socket fashion, the threads being configured to provide for effective tightening together of the segments during actual drilling. In order to insert an extension segment it is thus required to loosen the two adjacent connected segments, between which the extension segment must be inserted, with respect to one another, such loosening permitting separation of the segments. It is this loosening operation that often presents difficulties and that requires the use of a special wrench, hereinafter referred to as a drill bit wrench. The same difficulties occur also when a drill bit is withdrawn from a hole drilled and extension segments must be removed from the drill bit, which, in effect, requires a reverse operation to that required for inserting extension segments in line with a drill bit.
Known drill bit wrenches generally have a pair of opposing jaws, between which a drill bit segment can be gripped, and a lever that is displaceable for acting on the jaws and thereby for rotating a drill bit segment gripped between the jaws. Preferred wrenches of the type provide for the jaws to be pivotally connected to one another and for the lever to extend from one of the jaws, in a configuration in which displacement of the lever will enhance the gripping force of the jaws on the drill bit segment gripped between them. However, the gripping force that can be applied on a drill bit segment with known drill bit wrenches have not proved sufficient in all cases for loosening adjacent drill bit segments with respect to one another, the jaws tending to slip with respect to a drill bit segment gripped between them and thus not permitting required loosening.
It is accordingly an object of this invention to provide an improved drill bit wrench for loosening adjacent drill bit segments of a drill bit with respect to one another, as herein envisaged.
According to the invention there is provided a drill bit wrench for loosening a drill bit segment of a drill bit, having a diameter falling within a predetermined diameter range, with respect to an adjacent drill bit segment, which comprises
a gripping arm that has two ends and that defines an open mouth formation between the said two ends that permit the arm to be located around the drill bit segment to be loosened; and
a lever that is pivotally connected to and that extends from one end of the gripping arm,
and in which, with the gripping arm located around the drill bit segment to be loosened and with respect to a reference line extending from the pivot axis defined by the pivotal connection between the lever and the said one end of the gripping arm, through the longitudinal axis defined by the drill bit segment and the other end of the gripping arm, the gripping arm has a gripping formation, near the said other end of the gripping arm and that opposes the drill bit segment, on each side of the said line and the lever defines a convex wedge face that, by initial displacement of the lever in a direction that coincides with the required direction of rotation of the drill bit segment for loosening the drill bit segment, can wedge against the drill bit segment, acting on the drill bit segment in the region of the segment immediately adjacent the location where the said reference line intersects the face of the drill bit segment, for urging the drill bit segment into gripping engagement with the gripping formations and for permitting loosening of the drill bit segment with respect to an adjacent drill bit segment by continued displacement of the lever.
The gripping formations of the gripping arm each may comprise a gripping bit located within the gripping arm and defining an exposed, serrated face into which a drill bit segment can be urged for the gripping engagement thereof by the gripping formation.
The gripping formations may be located to engage a drill bit segment in locations of the segment that fall between two limit positions determined by the locations where two lines, extending respectively from the pivotal axis between the gripping arm and the lever at an angle of 12xc2x0 with respect to the reference line, on opposite sides of the reference line, intersect the drill bit segment on the side thereof where the gripping formations oppose the drill bit segment. Preferably, the gripping formations are located to engage a drill bit segment in locations of the segment that coincide substantially with the locations where two lines, extending respectively from the pivotal axis between the gripping arm and the lever at an angle of 8xc2x0 with respect to the reference line, on opposite sides of the reference line, intersect the drill bit segment on the side thereof where the gripping formations oppose the drill bit segment.
The convex wedge face defined by the lever particularly may be profiled to act on a drill bit segment in a region of the segment defined between locations where the said reference line and a line extending from the pivotal axis between the gripping arm and the lever at an angle of 12xc2x0 with respect to the reference line, intersect the drill bit segment. Preferably, the convex wedge face defined by the lever is profiled to act on a drill bit segment in the region of the segment defined between locations where the said reference line and a line extending from the pivotal axis defined between the gripping arm and the lever at an angle of 8xc2x0 with respect to the reference line, intersect the drill bit segment.
The drill bit wrench of the invention further may include a primary displacement means that can act on the lever for displacing the lever. The primary displacement means particularly is a piston/cylinder arrangement.
The drill bit wrench further may include a secondary displacement means whereby the gripping arm can be displaced with respect to the lever, for locating the gripping arm around a drill bit segment. The secondary displacement means also may be a piston/cylinder arrangement.
Still further according to the invention, the lever may have an extension piece adjustably engaged therewith near the end of the lever remote from the end pivotally connected with the gripping arm, the extension piece rendering the length of the lever adjustable. The drill bit wrench particularly includes more than one extension piece with the extension pieces permitting replacement of one another for accommodating different applications of the drill bit wrench.
In use of the drill bit wrench of the invention and with the mouth of the gripping arm located around a drill bit segment to be loosened with respect to another segment, the displacement of the lever with respect to the gripping arm will provide for effective gripping of the drill bit segment by the gripping formations of the gripping arm, with continued displacement of the lever providing for loosening of the drill bit segment as required. As the force required for loosening a drill bit segment with respect to another increases, the action of the lever on the drill bit segment urging it into gripping engagement with the gripping formations of the gripping arm also will increase, particularly to the extent that the gripping engagement of the drill bit segment will be such that slipping between the gripping formations and the drill bit segment cannot occur and loosening of the drill bit segment is permitted without undue difficulties.